The present invention relates to an improved method for the attachment of a tension rod to an open end of a cable by the employment of a heat shrinkable plastic cap that is utilized to encapsulate the cable end in which the tension rod is partially inserted, and to uniformly force a casting resin within the plastic cap about the tension rod and into the cable core.
Tension rods attached to communication cables are priorly known for achieving a convenient means for pulling such cables through cable conduits in the installation of the communications systems. A principal reqirement for performing such cable pulling is that the pulling force applied to the tension rod be transmitted to substantially the same degree to the cable core and to the cable jacket so as to avoid any differential longitudinal movement or slippage between the cable core and the cable jacket as the cable is pulled through the cable conduit. Additionally, it is advantageous that the open end of the cable be sealed pressure tight, and that the mechanism for attaching the tension rod to the end of the cable have maximum cross-sectional dimensions that approximate that of the cable itself so as to permit the cables to be pulled through the cable conduits whose cross-sectional dimensions approximate that of the cables.
Priorly known techniques for attaching tension rods to cables have included the insertion of tension rods into cable cores and the provision of metallic caps having dimensions approximating that of the cable jackets so as to permit attachment thereto. The prior art metallic caps so employed were by necessity first joined with the cable jackets to form a hermetic seal in a separate operation, and subsequently the casting resins were forced under pressure into the metallic caps through lateral offset openings or valves in the caps. These procedures led to additional expense and were characterized by non-uniform distribution of the casting resins into the cable cores doe to the resin feed from one side of the metallic cap. Further, such prior art metallic caps had to be of sizes in conformence with the various cable jacket sizes, thus a large number of different sized metallic caps had to be retained in inventory.
An object of the instant invention is to provide an improved method for attaching a tension rod to a cable end in a manner that the overall cross-sectional dimensions of the assemblage is substantially that of the cable per se. A further object is to provide a tension rod cable assemblage wherein the tension rod is so attached to the cable that a pulling force applied to the tension rod is distributed between the cable core and the cable jacket in a manner to avoid differential longitudinal movement or slippage between the cable core and cable jacket. Additionally, an object of the invention is to provide an improved method whereby substantially all of the casting resin included in the encapsulating plastic cap is pressed into the cable core as distinguished from remaining in the cap chamber, thus providing a more secure mounting of the tension rod in the cable core.
The manner of achieving the objectives of the instant invention is to partially extend one end of a tension rod into a cable core, hold the combination of cable and rod in a vertical position, and move a heat shrinkable plastic cap containing a casting resin therein up from below the tension rod until the upper end of the plastic cap engages a portion of the cable jacket. Then heating first the upper portion of the plastic cap which causes a shrinking of the upper portion of the plastic cap so as to engage the adjacent portion of the cable jacket to form a hermetic seal therebetween, and then heating the lower portion of the plastic cap to cause a shrinking of the cap chamber which results in a uniform distribution of substantially all of the casting resin into the cable core.
The method in accordance with the instant invention enables the utilization of a very simple constructural configurations, for example, the tension rod may consist of a serrated pointed section for insertion in the cable core and eye at the opposite end. At the time that the tension rod is inserted in the cable core there are no confining external forces applied to the cable by an already mounted cap attached to the cable jacket. The shrinking of the plastic cap caused by the application of heat thereto results in a cap configuration which at one end is determined by the diameter of the cable jacket, and at the other end substantially by the dimensions of the tension rod. No valve in the plastic cap is required for the insertion of the casting resin and, accordingly, no dimensional aberrations are caused thereby. The heating steps may be practiced with simple tools such as a soldering iron available at construction sights. Since the plastic cap after the completion of the heat application step fully encapsulates the cable end and the extending portion of the tension rod, corrosion protection is provided to the complete tension rod cable assemblage. At the time that a pulling force is to be applied to the tension rod, a portion of the plastic cap is removed so as to provide free access to the tension eye of the rod.
Various other objects of the invention will become clear from the following descriptions of the preferred embodiments thereof, and the novel features will be particularly pointed out in connection with the appended claims.